Lock is the devil-costumed member of Lock, Shock, and Barrel, Halloween Town’s three-person argument against giving children access to a walking bathtub.

Disney identifies Lock as the member who considers himself the leader of the trio. That confidence does not necessarily mean Shock agrees, especially since she is officially described as the cleverest of the three. Lock nevertheless approaches their schemes with the certainty of someone who believes possession of a devil mask has established a valid chain of command.

In The Nightmare Before Christmas, Jack Skellington recruits Lock, Shock, and Barrel to kidnap Santa Claus. Jack specifically warns them to leave Oogie Boogie out of the plan. Naturally, they deliver Santa directly to Oogie Boogie.

Lock’s individual identity is deliberately simple. He wears the red devil costume, pushes himself forward as leader, trades insults and ideas with Shock and Barrel, and joins the trio’s various acts of enthusiastic seasonal misconduct. The movie does not provide him with hidden powers, elaborate history, or a solo character arc, so none needs to be invented.

Lock works because the trio works.

Shock has the brains. Barrel has the skeleton suit.

Lock has apparently declared himself management.